The ebolaviruses and Marburg virus (MARV) constitute the family Filoviridae (filoviruses) that cause severe hemorrhagic fever with human case fatalities of 50-90%. The current epidemic in West Africa, unprecedented in terms of geographic scope and size, highlights the continued need for development of therapeutics. Among the five ebolavirus species, the Zaire and Sudan subtypes (EBOV and SUDV, respectively) are the most pathogenic and both have resulted in recurring outbreaks. Together, EBOV and SUDV accounted for over 95% of Ebola-related deaths from 1976-2012. In addition, another ebolavirus subtype, the Bundibugyo virus (BDBV), has caused two sizable outbreaks in 2007 and 2012. Current filovirus antibody therapies are narrowly strain specific, and therefore have limited therapeutic utility. The goal of this proposal is to use an innovative antibody technology platform, bispecific antibody (Bis-mAb) engineering, to develop cross-neutralizing, therapeutic antibody cocktails effective against EBOV, SUDV, and BDBV. We have produced several bispecific monoclonal antibodies (Bis-mAbs) that can effectively neutralize EBOV and SUDV, binding to a critical neutralization epitope at the viral glycoprotein (GP) base, as well as a suite of novel cross-reactive antibodies binding multiple filovirus species. Notably, one of these mAbs has shown in vivo protection in both EBOV and SUDV murine infection models. This is the first report of a filovirus cross-protective antibody. Our preliminary data also reveal a series of novel, conserved epitopes within the glycan cap and the fusion loop of filovirus GP. We hypothesize that these key epitopes can be exploited in a synergistic manner when targeted by Bis-mAbs. Taking advantage of the enhanced avidity and synergistic neutralization that result from targeting multiple key epitopes, such Bis-mAbs will represent a novel class of highly effective, broadly neutralizing filovirus therapeutics. In Aim 1, we will explore GP base binding Bis-mAb designs to optimize potency, and test them for neutralization in combination with a cross-binding antibody that engages a second epitope in the glycan cap. Aim 2 will focus on developing novel Bis-mAbs that target new, highly conserved epitopes on GP that are present in multiple filovirus species. The Bis-mAbs will be tested for enhanced and broad neutralizing activity against EBOV, SUDV, and BDBV to select 3-5 lead therapeutic candidates. Phase I studies will lay the foundation for the anticipated Phase II component, in which the most potent combinations of Bis-mAbs will be evaluated for their ability to protect in vivo. This approach can further be extended to create novel Bis-mAb cocktails that can target all filovirus species including MARV. This work represents a partnership between academic (Einstein) and commercial (Integrated BioTherapeutics) entities to develop cross-neutralizing, therapeutic Bis-mAb cocktails. The approach leverages proprietary antibodies, technology platforms, and complementary expertise from both partners. These therapies will fill a major therapeutic gap and could not be obtained using conventional antibody isolation methods.